1. Technical Field
This invention relates generally to the batch processing of miniature electronic circuit components, including passive, two-terminal, ceramic capacitors, resistors, inductors, and the like. More particularly, it concerns a contactor assembly for electrically contacting a terminal on such a component or other device under test (DUT) as part of the batch processing for purposes of parametric testing.
2. Description of Related Art
The tiny size of electronic circuit components of interest herein complicates processing. Typically fabricated in parallelepiped shapes having dimensions as small as 0.020″ by 0.010″ by 0.010,″ more or less, these difficult-to-handle components require appropriate equipment and precision handling techniques. What is sometimes referred to as a “carrier plate” holds many hundreds of the components upright in spaced-apart positions as the ends of each component are coated with a conductive material to produce electrical terminals. After adding terminals, a “test plate” holds the large batch of components for movement past a contactor assembly of a testing system for parametric testing purposes and eventual sorting. Thoughtful design of each of these components promotes efficient processing. Reference may be made to U.S. Pat. Nos. 6,204,464; 6,294,747; 6,194,679; 6,069,480; 4,395,184; and 4,669,416 for examples of some prior art component handling systems and testing techniques.
The contactor assembly is of particular interest. It is a device having an electrical contact (an electrically conductive member) that touches the DUT terminal as the test plate moves the DUT past the contactor assembly. It does so to complete an electrical testing circuit. One problem is that touching the DUT terminal improperly can physically damage the terminal. It can also produce a poor electrical contact that degrades test results.
Existing production testers often use “sliding contacts,” “rolling contacts,” and/or “pogo pin contacts” to perform the electrical and mechanical functions. Electrically, the contacts should couple a test signal between testing components and the DUT terminal in a manner providing a sufficiently accurate electrical test. Mechanically, the contacts should press the contact against the DUT terminal with enough force to attain a good electrical contact despite the usual presence of a non-conductive oxide layer on the surface of the DUT terminal. Sufficient force causes the contact (e.g., a sliding leaf spring type of contact) to advance through the oxide layer to the underlying conductive material of the DUT terminal, and that reduces electrical resistance between the contact and the DUT terminal.
One problem is that forcing the contact against the DUT terminal can leave a mark or scratch on the surface of the DUT terminal. End users of the component often consider such scratches to be defects. Failure to achieve a good electrical contact, on the other hand, degrades test results. The electrical and mechanical functions are conflicting in those respects and existing contactor assembly designs exhibit varying degrees of success in alleviating the conflict. Thus, manufacturers engaged in batch processing of miniature electronic circuit components seek improvement in contactor assembly design and so a need exists for a better contactor assembly.
U.S. patent application Ser. No. 10/097,464 filed Mar. 14, 2002 and issued as U.S. Pat. No. 6,756,798 addresses the concerns outlined above. It describes a contactor assembly having at least three independently moveable contacts in side-by-side relationship that are spring biased toward the DUT terminal. Such a contactor assembly is sometimes referred to as a multi point contactor (MPC). Three independently moveable contacts help insure that at least two of the contacts make electrical contact with the DUT terminal for lower serial impedance in series with the effective serial resistance (ESR) of the DUT. Preferably, spring biasing results in a constant-force over a normal range of travel (e.g., one to three millimeters) so that one contact does not dominate and hinder electrical contact by the others. Thus, a constant, predictable force is important to proper functioning, and so further MPC technology refinements are desirable in that respect.
This invention addresses the need outlined above by providing an MPC assembly and contact or blade construction having an integral spring that is formed as a part of the blade (e.g., laser machined or chemically etched). The blade is laser machined from a sheet of electrically conductive material to include the integral spring. Fabrication is precise, repeatable, and conveniently varied for different spring characteristics. In operation, the blade is spring biased toward the DUT independent of the other blades, but with a uniform force over a nominal range of travel that is common to all the blades.
To paraphrase some of the more precise language appearing in the claims and further introduce the nomenclature use, a contactor assembly constructed according to the invention includes a contact-holding structure that holds at least contacts three contacts (also referred to as blades). At least one of the contacts includes an integral spring (i.e., a spring portion of the contact). Preferably, that contact is in the form of a blade fabricated from a sheet of electrically conductive material to include a first portion for bearing against the contact-holding structure (directly or indirectly via an external spring), a second portion for bearing against the terminal on the DUT, and a third portion interconnecting the first and second portions. The third portion is shaped and dimensioned (i.e., adapted) to function as an integral spring for spring biasing the second portion away from the first portion toward the terminal on the DUT. Preferably, the third portion of the blade has a serpentine shape blade that achieves desired constant-force spring characteristics over a nominal range of blade travel.
In line with the above, a method for fabricating blades for a component testing system contactor assembly includes the step of providing a sheet of electrically conductive material. The method proceeds by forming an array of blades in the sheet of electrically conductive material (e.g., by laser-machining or chemical etching the sheet) such that each blade includes (i) a first portion for bearing against the contact-holding structure, (ii) a second portion for bearing against the terminal on the DUT, and (iii) a third portion interconnecting the first and second portions as an integral spring having desired spring characteristics. The array of blades is then separated into individual blades. The size and shape fabricated may be adjusted empirically or theoretically to result in different spring characteristics.
Thus, the invention significantly improves MPC technology with a constant-force, integral-spring, MPC blade construction. The MPC assembly can have many blades, each with its own integral spring so that all blades can contact the surface of the DUT. Very low force is achieved. It is a constant force. By using thin blades with no external springs, with the blades spaced as desired by identically shaped insulating spacers, there is virtually no limit to the number of electrical contacts that can be made to the DUT terminal. The following illustrative drawings and detailed description make the foregoing and other objects, features, and advantages of the invention more apparent.